Vacuum processing apparatus

ABSTRACT

A wafer conveyor system for used in a vacuum processing apparatus wherein the conveyor structure is provided with a transfer structure and a robot apparatus is arranged on the transfer structure. The robot provides for rotation of the wafer horizontally from a position in a cassette to an opposite postion of the cassette.

This application is a Divisional application of application Ser. No. 09/766,587, filed Jan. 23, 2001, which is a Divisional application of application Ser. No. 09/461,432, filed Dec. 16, 1999, now U.S. Pat. No. 6,330,755 which is a Continuation application of application Ser. No. 09/177,495, filed Oct. 23, 1998, now U.S. Pat. No. 6,012,235 which is a Continuation application of application Ser. No. 09/061,062, filed Apr. 16, 1998, now U.S. Pat. No. 5,950,330 which is a Continuation application of application Ser. No. 08/882,731, filed Jun. 26, 1997, now U.S. Pat. No. 5,784,799 which is a Divisional application of application Ser. No. 08/593,870, filed Jan. 30, 1996, now U.S. Pat. No. 5,661,913 which is a Continuing application of application Ser. No. 08/443,039, filed May 17, 1995, now U.S. Pat. No. 5,553,396, which is a Divisional application of application Ser. No. 08/302,443, filed Sep. 9, 1994, now U.S. Pat. No. 5,457,896, which is a Continuing application of application Ser. No. 08/096,256, filed Jul. 26, 1993, now U.S. Pat. No. 5,349,762 which is a Continuing application of application Ser. No. 07/751,952, filed Aug. 29, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vacuum processing apparatus and operating method therefor. More specifically, the present invention relates to a vacuum processing apparatus having vacuum processing chambers the inside of which must be cleaned, and its operating method.

2. Description of the Prior Art

In a vacuum processing apparatus such as a dry etching apparatus, a CVD apparatus or a sputtering apparatus, a predetermined number of substrates to be treated are stored as one unit (which is generally referred to as a “lot”) in a substrate cassette and are loaded in the apparatus. The substrates after being processed are likewise stored in the same unit in the substrate cassette and are recovered. This is an ordinary method of operating these apparatuses to improve the productivity.

In such a vacuum processing apparatus described above, particularly in an apparatus which utilizes a reaction by an active gas, as typified by a dry etching apparatus and a CVD apparatus, reaction products adhere to and are deposited on a vacuum processing chamber with the progress of processing. For this reason, problems such as degradation of vacuum performance, the increase of dust, the drop of the levels of optical monitoring signals occur. To solve these problems, conventionally the insides of the vacuum processing chambers are cleaned periodically. Cleaning operations include so-called “wet cleaning” which is wiping-off of the adhering matters by use of an organic solvent, etc., and so-called “dry cleaning” in which an active gas or plasma is used for decomposing adhering matters. Dry cleaning is superior from the aspect of the working factor and efficiency. These features of the dry cleaning have become essential with the progress in automation of production lines.

An example of vacuum processing apparatuses having such a dry cleaning function is disclosed in Japanese Utility Model Laid-Open No 127125/1988. This apparatus includes a preliminary vacuum chamber for introducing wafers to be treated into a processing chamber from an atmospheric side to a vacuum side, which is disposed adjacent to the processing chamber through a gate valve, dummy wafers are loaded in the preliminary vacuum chamber and are transferred into the processing chamber by exclusive conveyor means before the processing chamber is subjected to dry cleaning, and the dummy wafer is returned to the vacuum preparatory chamber by the conveyor means after dry cleaning is completed.

SUMMARY OF THE INVENTION

In the prior art technology described above, the structure of the vacuum processing apparatus is not much considered. The preliminary vacuum chamber for storing the dummy wafers must have a large capacity, the exclusive conveyor means is necessary for transferring the dummy wafers and thus, the apparatus is complicated in structure.

Dummy wafers used for plasma cleaning are again returned to the preliminary vacuum chamber and are made to stand by. In this instance, reaction products generated during plasma cleaning and residual gas used for plasma cleaning adhere on the used dummy wafers. Thereafter, normal processing for wafers is resumed. Therefore, the used dummy wafers and unprocessed wafers exist in mixture inside the preliminary vacuum chamber and this state is not desirable from the aspect of contamination of unprocessed wafers.

The present invention provides a vacuum processing apparatus which solves the problems described above, is simple in structure, prevents contamination of unprocessed substrates and accomplishes a high production yield. A vacuum processing apparatus having vacuum processing chambers the insides of which are dry-cleaned after substrates to be treated are processed in vacuum is provided with first storage means for storing substrates to be treated, second storage means for storing dummy substrates, the first and second storage means being disposed in the air, conveyor means for transferring the substrates to be processed between the first storage means and the vacuum processing chambers and for transferring the dummy substrates between the second storage means and the vacuum processing chambers, and control means for controlling the conveyor means so as to transfer the dummy substrates between the second storage means and the vacuum processing chambers before and after dry cleaning of the vacuum processing chambers. A method of operating a vacuum processing apparatus having vacuum processing chambers the insides of which are dry-cleaned after substrates to be processed are processed in vacuum comprises the steps of disposing first storage means for storing the substrates to be processed together with second storage means for storing dummy substrates in the air atmosphere, transferring the substrates to be processed between the first storage means and the vacuum processing chambers and vacuum-processing the substrates to be processed, and transferring the dummy substrates between the second storage means and the vacuum processing chambers before and after dry-cleaning of the vacuum processing chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a dry etching apparatus as an embodiment of a vacuum processing apparatus in accordance with the present invention; and

FIG. 2 is a vertical sectional view taken along line I—I of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As substrates to be processed are processed in a vacuum processing apparatus, reaction products adhere to and are deposited in vacuum processing chambers. The reaction products adhering to and deposited in the vacuum processing chambers are removed by disposing dummy wafers inside the vacuum processing chambers and by conducting dry-cleaning. To carry out dry cleaning, the timings of dry cleaning of the vacuum processing chambers are determined and during or after the processing of a predetermined number of substrates to be processed, dummy substrates are conveyed by substrate conveyor means from dummy substrate storage means disposed in the air atmosphere together with processed substrate storage means, and are then disposed inside the vacuum processing chambers After the dummy substrates are thus disposed, a plasma is generated inside each of the vacuum processing chambers to execute dry-cleaning inside the vacuum processing chamber. After dry-cleaning inside the vacuum processing chambers is completed, the dummy substrates are returned from the vacuum processing chambers to the dummy substrate storage means by the substrate conveyor means. In this manner, a preliminary vacuum chamber and an exclusive transfer mechanism both necessary in prior art techniques become unnecessary, and the apparatus structure gets simplified. The dummy substrates used for the dry-cleaning and the substrates to be processed do not co-exist inside the same chamber, so that contamination of substrates to be processed due to dust and remaining gas is prevented and a high production yield can be achieved.

Hereinafter, an embodiment of the present invention will be explained with reference to FIGS. 1 and 2.

FIGS. 1 and 2 show a vacuum processing apparatus of the present invention which is, in this case, a dry-etching apparatus for etching wafers, i.e., substrates to be processed by plasma.

Cassette tables 2 a to 2 c are disclosed in an L-shape in this case in positions such that they can be loaded into and unloaded from the apparatus without changing their positions and postures. In other words, the cassettes 1 a to 1 c are fixed always in predetermined positions on a substantially horizontal plane, while the cassette tables 2 a and 2 b are disposed adjacent to and in parallel with each other on one of the sides of the L-shape. The cassette table 2 c is disposed on the other side of the L-shape. The cassettes 1 a and 1 b are for storing unprocessed wafers and for recovering the processed wafers. They can store a plurality (usually 25) of wafers 20 as the substrates to be treated. The cassette 1 c in this case is for storing the dummy wafers for effecting dry-cleaning using plasma (hereinafter referred to as “plasma-cleaning”) and recovering the dummy wafers after plasma-cleaning. It can store a plurality of (usually twenty-five pieces) dummy wafers 30.

A load lock chamber 5 and unload lock chamber 6 are so disposed as to face the cassette tables 2 a and 2 b, and a conveyor 13 is disposed between the cassette tables 2 a, 2 b and the load lock chamber 5 and the unload lock chamber 6. The load lock chamber 5 is equipped with an evacuating device 3 and a gas introduction device 4, and can load unprocessed wafers in the vacuum apparatus through a gate valve 12 a. The unload lock chamber 6 is similarly equipped with the evacuating device 3 and the gas introduction device 4, and can take out processed wafers to the atmosphere through a gate valve 12 d. The conveyor 13 is equipped with a robot having X, Y, Z and - axes, which operates so as to deliver and receive the wafers 20 between the cassettes 1 a, 1 b and the load lock and unload lock chambers 5 and 6 and the dummy wafers 30 between the cassette 1 c and the load lock and unload lock chambers 5 and 6.

The load lock chamber 5 and the unload lock chamber 6 are connected to a transfer chamber 16 through the gate valves 12 b and 12 c. The transfer chamber 16 is rectangular, in this case, and etching chambers 11 a, 11 b and 11 c are disposed on the three side walls of the transfer chamber 16 through gate valves 15 a, 15 b and 15 c, respectively. A conveyor 14 capable of delivering the wafers 20 or the dummy wafers 30 from the load lock chamber 5 to the etching chambers 11 a, 11 b, 11 c and of delivering them from the chambers 11 a, 11 b, 11 c to the unload lock chamber 6 is disposed inside the transfer chamber 16. The transfer chamber 16 is equipped with an evacuating device 17 capable of independent evacuation.

The etching chambers 11 a, 11 b, 11 c have the same structure and can make the same processing. The explanation will be given on the etching chamber 11 b by way of example. The etching chamber 11 b has a sample table 8 b for placing the wafers 20 thereon, and a discharge chamber is so provided as to define a discharge portion 7 b above the sample table 8 b. The etching chamber 11 b includes a gas introduction device 10 b for introducing a processing gas in the discharge portion 7 b and an evacuating device 9 b for decreasing the internal pressure of the etching chamber 11 b to a predetermined pressure. The etching chamber 11 b further includes generation means for generating a microwave and a magnetic field for converting processing gas in the discharge portion 7 b to plasma.

A sensor 18 for measuring the intensity of plasma light is disposed at an upper part of the etching chamber. The measured value of the sensor 13 is inputted to a controller 19. The controller 19 compares the measured value from the sensor 18 with a predetermined one and determines the timing of cleaning inside the etching chamber. The controller 19 controls the conveyors 13 and 14 to control the transfer of the dummy wafers 30 between the cassette 1 c and the etching chambers 11 a to 11 c.

In a vacuum processing apparatus having the construction described above, the cassettes 1 a, 1 b storing unprocessed wafers are first placed onto the cassette tables 2 a, 2 b by a line transfer robot which operates on the basis of the data sent from a host control apparatus, or by an operator. On the other hand, the cassette 1 c storing the dummy wafers is placed on the cassette table 2 c. The vacuum processing apparatus executes the wafer processing or plasma cleaning on the basis of recognition by itself of the production-data provided on the cassettes 1 a to 1 c, of the data sent from the host control apparatus, or of the command inputted by an operator.

For instance, the wafers 20 are sequentially loaded in the order from above into the etching chambers 11 a, 11 b, 11 c by the conveyors 13 and 14, and are etched. The etched wafers are stored in their original positions inside the cassette 1 a by the conveyors 14 and 13. In this case, from the start to the end of the operation, without changing the position and posture of the cassettes, the unprocessed wafers are taken out from the cassettes and are returned in their original positions where the wafers have been stored, and are stored there. In this manner, the apparatus can easily cope with automation of the production line, contamination of the wafers due to dust can be reduced and high production efficiency and high production yield can thus be accomplished.

As etching is repeated, the reaction products adhere to and are deposited on the inner wall of the etching chambers 11 a to 11 c. Therefore, the original state must be recovered by removing the adhering matters by plasma cleaning. The controller 19 judges the timing of this plasma cleaning. In this case, a portion through which the plasma light passes is provided in each of the etching chambers 11 a to 11 c. The sensor 18 measures the intensity of the plasma light passing through this portion and when the measured value reaches a predetermined one, the start timing of plasma cleaning is judged. Alternatively, the timing of plasma cleaning may be judged by counting the number of wafers processed in each etching chamber by the controller 19 and judging the timing when this value reaches a predetermined value. The actual timing of plasma cleaning that is carried out may be during a processing of a predetermined number of wafers in the cassette 1 a or 1 b, after the processing of all the wafers 20 in a cassette is completed and before the processing of wafers in the next cassette.

Plasma cleaning is carried out in the following sequence. In this case, the explanation will be given about a case where the etching chambers 11 a to 11 c are subjected to plasma cleaning by using three dummy wafers 30 among the dummy wafers 30 (twenty-five dummy wafers are stored in this case) stored in the cassette 1 c.

Dummy wafers 30 which are stored in the cassette 1 c and are not used yet or can be used because the number of times of use for plasma cleaning is below a predetermined one are drawn by the conveyor 13. At this time, dummy wafers 30 stored in any position in the cassette 1 c may be used but in this case, the position numbers of the dummy wafers in the cassette and their number of times of use are stored in the controller 19, and accordingly dummy wafers having smaller numbers of times of use are drawn preferentially. Then, the dummy wafers 30 are loaded in the load lock chamber 5 disposed on the opposite side to the cassette 1 a by the conveyor 13 through the gate valve 12 a in the same way as the transfer at the time of etching of wafers 20. After the gate valve 12 a is closed, the load lock chamber 5 is evacuated to a predetermined pressure by the vacuum exhaust device 3 and then the gate valves 12 b and 15 a are opened. The dummy wafers 30 are transferred by the conveyor 14 from the load lock chamber 5 to the etching chamber 11 a through the transfer chamber 16 and are placed on the sample table 8 a. After the gate valve 15 a is closed, plasma cleaning is carried out in the etching chamber 11 a in which the dummy wafers 30 are disposed, under a predetermined condition.

In the interim, the gate valves 12 a, 12 b are closed and the pressure of the load lock chamber 5 is returned to the atmospheric pressure by the gas introduction device 4. Next, the gate valve 12 a is opened and the second dummy wafer 30 is loaded in the load lock chamber 5 by the conveyor 13 in the same way as the first dummy wafer 30, and evacuation is effected again by the evacuating device 3 to a predetermined pressure after closing the gate valve 12 a. Thereafter, the gate valves 12 b and 15 b are opened and the second dummy wafer 30 is transferred from the load lock chamber 5 to the etching chamber 11 b through the transfer chamber 16 by the conveyor 14. Plasma cleaning is started after the gate valve 15 b is closed.

In the interim, the third dummy wafer 30 is transferred into the etching chamber 11 c in the same way as the second dummy wafer 30 and plasma cleaning is carried out.

After plasma cleaning is completed in the etching chamber 11 a in which the first dummy wafer 20 is placed, the gate valves 15 a and 12 c are opened. The used dummy wafer 30 is transferred from the etching chamber 11 a to the unload lock chamber 6 by the conveyor 14. Then, the gate valve 12 c is closed. After the pressure of the unload lock chamber 6 is returned to the atmospheric pressure by the gas introduction device 4, the gate valve 12 d is opened. The used dummy wafer 30 transferred to the unload lock chamber 6 is taken out in the air by the conveyor 13 through the gate valve 12 d and is returned to its original position in the cassette 1 c in which it is stored at the start.

When plasma cleaning of the etching chambers 11 b and 11 c is completed, the second and third dummy wafers 20 are returned to their original positions in the cassette 1 c.

In this way, the used dummy wafers 30 are returned to their original positions in the cassette 1 c and the dummy wafers 30 are always stocked in the cassette 1 c. When all the dummy wafers 30 in the cassette 1 c are used for plasma cleaning or when the numbers of times of use of the wafers 30 reach the predetermined ones after the repetition of use, the dummy wafers 30 are replaced as a whole together with the cassette 1 c. The timing of this replacement of the cassette is managed by the controller 19 and the replacement is instructed to the host control apparatus for controlling the line transfer robot or to the operator.

Although the explanation given above deals with the case where the etching chambers 11 a to 11 c are continuously plasma-cleaned by the use of three dummy wafers 30 among the dummy wafers 30 in the cassette 1 c, other processing methods may be employed, as well.

For example, the etching chambers 11 a to 11 c are sequentially plasma-cleaned by the use of one dummy wafer 30. In the case of such plasma cleaning, unprocessed wafers 20 can be etched in etching chambers other than the one subjected to plasma cleaning, and plasma cleaning can thus be carried out without interrupting etching.

If the processing chambers are different, for example, there are an etching chamber, a post-processing chamber and a film-formation chamber, and wafers are sequentially processed while passing through each of these processing chambers, each of the processing chambers can be subjected appropriately to plasma cleaning by sending dummy wafers 30 during the processing of the wafers 20 which are stored in the cassette 1 a or 2 a and drawn and sent sequentially, by passing merely the dummy wafers 30 through the processing chambers for which plasma cleaning is not necessary, and by executing plasma cleaning only when the dummy wafers 30 reach the processing chambers which need plasma cleaning.

According to the embodiment described above, the cassette storing the dummy wafers and the cassettes storing the wafers to be processed are disposed together in the air, the dummy wafers are loaded from the cassette into the apparatus by the same conveyor as the conveyor for transferring the wafers, at the time of cleaning, and the used dummy wafers are returned to their original positions in the cassette. In this way, a mechanism for conducting exclusively plasma cleaning need not be provided, and the construction of the apparatus can be simplified. It is not necessary to handle plasma cleaning as a particular processing sequence, but the plasma cleaning can be incorporated in an ordinary etching processing and can be carried out efficiently in a series of operations.

The dummy wafers used for plasma cleaning are returned to their original positions in the cassette placed in the air. Accordingly, the used dummy wafers and the wafers before and after processing do not exist mixedly in the vacuum chamber, so that contamination of wafers due to dust and remaining gas does not occur unlike conventional apparatuses.

The used dummy wafers are returned to their original positions in the cassette and the numbers of times of their use is managed. Accordingly, it is possible to prevent the confusion of the used dummy wafers with the unused dummy wafers and the confusion of the dummy wafers having small numbers of times of use with the dummy wafers having large numbers of times of use. For these reasons, the dummy wafers can be used effectively without any problem when plasma cleaning is carried out.

Furthermore, in accordance with the present invention, the apparatus can have a plurality of processing chambers and can transfer wafers and dummy wafers by the same conveyor. Since plasma cleaning can be carried out by managing the timing of cleaning of each processing chamber by the controller, the cleaning cycle can be set arbitrarily, dry cleaning can be carried out without interrupting the flow of the processing, the processing can be efficiently made and the productivity can be improved.

As described above, according to the present invention, there are effects that the construction of the apparatus is simple, the substrates to be processed are free from contamination and the production yield is high. 

What is claimed is:
 1. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette table for holding the cassette; a second conveyor structure for transferring a wafer; a vacuum loader provided with a conveyor chamber and a third conveyor structure; at least one vacuum processing chamber; and a lock chamber disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to a cassette table, exposed to the air, the first conveyor structure is adapted to travel parallel to the second conveyor structure, and the first robot is adapted to transfer the cassette from the cassette holder onto the cassette table.
 2. A vacuum processing system, comprising: a first conveyor structure provided with a first robot for transferring a cassette; a cassette mount unit for holding the cassette; a second conveyor structure for transferring a wafer held in the cassette on the cassette mount unit; a vacuum loader provided with a conveyor chamber, a third conveyor structure and at least one vacuum processing chamber; and a set of lock chambers disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure, the cassette mount unit, the second conveyor structure, the set of lock chambers and the vacuum loader are arranged in tandem in series, the second conveyor structure is disposed between a set of two cassettes and the set of lock chambers, the set of lock chambers including a chamber to take in and to take out a wafer one by one, and another chamber to take in and to take out a processed wafer, the second conveyor structure is provided with a second robot extendable to the wafer horizontally located in the lock chambers, the lock chambers are each provided with both an inlet and an outlet located in a horizontal line, and the second robot faces to a set of wafers disposed in the cassette and transfers the wafers one by one to a lock chamber in which one wafer is to be disposed, and a third robot, of the third conveyor structure is disposed in the conveyor chamber of the vacuum loader so as to face to the lock chambers.
 3. The vacuum processing system according to claim 2, wherein the second robot is adapted to travel on a track.
 4. The vacuum processing system according to claim 3, wherein the vacuum loader is provided with a set of vacuum processing chambers which are arranged around said conveyor chamber.
 5. The vacuum processing system according to claim 3, wherein the second robot is arranged so as to travel in parallel to a traveling direction of the first conveyor structure.
 6. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette mount unit for holding the cassette; a second conveyor structure for transferring a wafer held in the cassette on the cassette mount unit; a vacuum loader provided with a conveyor chamber, third conveyor structure, and at least one vacuum processing chamber; and a set of lock chambers disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure, the cassette mount unit, the second conveyor structure, the set of lock chambers and the vacuum loader are arranged in tandem in series, the second conveyor structure is disposed between the cassette mount unit and the set of lock chambers which comprise a chamber to take in and to take out a wafer one by one, and another chamber to take in and to take out a processed wafer, the second conveyor structure is provided with a second robot extendable to the wafer horizontally located and to the lock chambers, and the lock chambers are each provided with an inlet and an outlet located in a horizontal line, and a third robot is disposed in the conveyor chamber of the vacuum loader and provided with an arm extendable into the lock chambers.
 7. The vacuum processing system according to claim 6, wherein the cassette mount unit has a cassette positioning plane which is a substantially horizontal plane, and the cassette positioning plane is oriented such that a cassette is placed on and moved from the cassette positioning plane so as to maintain a surface of the wafer to be processed substantially horizontal.
 8. The vacuum processing system according to claim 6, wherein the second robot has a wafer positioning plane which is a substantially horizontal plane, and the wafer positioning plane is oriented such that a wafer is placed on and moved from the wafer positioning plane so as to maintain a surface of a wafer to be processed substantially horizontal.
 9. The vacuum processing system according to claim 6, wherein the third robot has a wafer positioning plane which is a substantially horizontal plane, and the wafer positioning plane is oriented such that the wafer is placed on and moved from the wafer positioning plane so as to maintain a surface of a wafer to be processed substantially horizontal.
 10. The vacuum processing system according to claim 6, wherein the at least one vacuum processing chamber includes an etching chamber, a post-processing chamber and a film-formation chamber, and wafers are sequentially processed while passing through each of these processing chambers.
 11. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette mount unit for holding the cassette; a second conveyor structure for transferring a wafer held in the cassette on the cassette mount unit; a vacuum loader provided with a conveyor chamber, a third conveyor structure and at least one vacuum processing chamber; and a set of lock chambers disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to the cassette mount unit, the cassette mount unit is provided with a set of cassette tables exposed to the air, the first robot is adapted to transfer, exposed to the air, a cassette to each of the cassette tables, the first robot is adapted to transfer the cassette from the cassette holder onto a cassette table in a state that a window portion of the cassette, through which wafers are removed from the cassette, faces to the set of lock chambers and a portion of the cassette opposite to the window portion faces to the first conveyor structure, and the second conveyor structure is disposed between a set of two cassettes and a set of the lock chambers which comprises a chamber to take in and to take out a wafer one by one, and another chamber to take in and to take out a processed wafer.
 12. The vacuum processing system according to claim 11, wherein the cassette mount unit is provided with a set of two cassette tables, each of which holds one cassette.
 13. The vacuum processing system according to claim 12, wherein the set of lock chambers includes a set of a load lock chamber and an unload lock chamber, and the set of cassette tables confront to the set of load lock chamber and unload lock chamber through the second conveyor structure.
 14. The vacuum processing system according to claim 11, wherein the second conveyor structure is provided with a second robot, which takes out, exposed to the air, a wafer from a cassette held on the cassette mount unit.
 15. The vacuum processing system according to claim 11, wherein the first conveyor structure travels on a track, and the set of cassette tables are arranged in parallel to the track.
 16. The vacuum processing system according to claim 11, wherein each of the cassettes is provided with a window open to the second conveyor structure, large enough to take out a wafer from the cassette.
 17. The vacuum processing system according to claim 16, wherein the second robot is adapted to transfer a wafer from the cassette mount unit to a lock chamber, of the set of lock chambers, without changing a horizontal plane of the wafer.
 18. The vacuum processing system comprising: a first conveyor structure for transferring a cassette; a cassette mount unit for holding the cassette, the cassette mount unit having at least one cassette table; a second conveyor structure for transferring a wafer in the cassette held on the cassette mount unit; a vacuum loader provided with a conveyor chamber, a third conveyor structure and at least one vacuum processing chamber; and lock chambers disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to a cassette table, of the cassette mount unit, exposed to the air, the cassette mount unit is provided with a set of cassette tables, each of which is adapted to hold one cassette, the second conveyor structure is provided with a second robot, the second robot being adapted to travel along a traveling direction of the first conveyor structure and traveling on a track of the second conveyor structure, the set of lock chambers includes a load lock chamber and a separate unload lock chamber, the third conveyor structure includes a third robot which transfers a wafer from the load lock chamber to the conveyor chamber and a processed wafer from the conveyor chamber to the unload lock chamber, the first robot, the second robot and the third robot are arranged in tandem in the direction perpendicular to the traveling direction of the first conveyor structure, and the set of lock chambers is provided with both an inlet nd an outlet located in a horizontal line, and the third robot is disposed in the conveyor chamber of the vacuum loader and provided with an arm extendable into the set of lock chambers.
 19. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette mount unit for holding a cassette, the cassette mount unit having at least one cassette table; a second conveyor structure for transferring a wafer in a cassette held on the cassette mount unit; a vacuum loader provided with a conveyor chamber, a third conveyor structure and at least one vacuum processing chamber; and a set of lock chambers disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to a cassette table of the cassette mount unit, exposed to the air, the cassette mount unit is provided with a set of two cassette tables, each of which holds one cassette, the second conveyor structure is provided with a second robot, the second robot being adapted to travel in a traveling direction of the first robot on a track of the first conveyor structure, the set of lock chambers includes a load lock chamber and a separate unload lock chamber, the third conveyor structure includes a third robot which is adapted to transfer a wafer from the load lock chamber to the conveyor chamber and a processed wafer from the conveyor chamber to the unload lock chamber, and the wafer is transferred from a cassette on the cassette mount table to the vacuum processing chamber by the second robot and the third robot in a state that a horizontal line is kept in the extent of one cassette height during transportation of the wafer.
 20. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette table for holding the cassette; a second conveyor structure for transferring a wafer; a vacuum loader provided with a conveyor chamber and a third conveyor structure; at least one vacuum processing chamber; and a lock chamber disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to a cassette table, exposed to the air, the first conveyor structure is adapted to travel parallel to the lock chamber over the longitudinal length of the lock chamber, and the first robot is adapted to transfer the cassette from the cassete holder onto the cassette table.
 21. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette table for holding the cassette; a second conveyor structure for transferring a wafer; a vacuum loader provided with a conveyor chamber and a third conveyor structure; at least one vacuum processing chamber; and a lock chamber disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to a cassette table, exposed to the air, and the first conveyor structure is adapted to transfer a cassette containing processed wafers, on the cassette table, to the cassette holder of the first conveyor structure, and the first robot is adapted to transfer the cassette from the cassette holder onto the cassette table.
 22. A vacuum processing system, comprising: a first conveyor structure for transferring a cassette; a cassette table for holding a cassette; a second conveyor structure for transferring a wafer; a vacuum loader provided with a conveyor chamber and a third conveyor structure; at least one vacuum processing chamber; and a lock chambers disposed between the second conveyor structure and the vacuum loader, wherein: the first conveyor structure is provided with a cassette holder and a first robot for transferring the cassette from the cassette holder to a cassette table, exposed to the air, the cassette holder of the first conveyor structure being adapted to carry a pair of cassettes, the first robot is adapted to transfer the cassette from the cassette holder onto the cassette table. 